The studies that led to this invention were funded under Grant Agreement No. CSJU-GAM-SAGE-2008-001 as part of the European Union's Seventh Framework Program (FP7/2007-2013) for the Clean Sky Joint Technology Initiative.
The present invention relates to an inner ring for an adjustable guide vane assembly, an inner ring segment for such an inner ring, a guide vane, a guide vane assembly, and a turbomachine.
Turbomachines, such as aircraft engines and stationary gas turbines, often have at least one guide vane assembly for adjustment of optimal operating conditions. Said guide vane assembly comprises an inner ring and a plurality of guide vanes, one end of each of which is arranged at the inner ring and which extend radially outward from it; the terms “radially,” “axially,” and “in the peripheral direction” always refer in this document—unless otherwise stated—to a central geometric axis of the guide vane assembly or of the inner ring and, for better readability, this is not always especially formulated.
Such a guide vane assembly can be designed, in particular, to be adjustable. In this case, the guide vanes can pivot around a provided pivot axis, which, in general, coincides with the longitudinal axis of the guide vanes and is directed essentially radially.
The pivoting can occur via outer adjusting components at the guide vanes, in particular by means of adjusting pins, which are inserted into or will be inserted into associated uptakes of the housing and which can then interact with a corresponding adjusting device at the outer housing.
An inner stabilization of the guide vanes often occurs in known guide vane assemblies via bearing pins, which extend radially inward from a respective guide vane plate and which can be guided in bearing bushings of the inner ring.
Especially in the case of relatively small turbomachines, it is possible in the case of a guide vane assembly concept that provides for guide vanes with guide vane plates and bearing pins, normally to provide only relatively few guide vanes on account of the small installation space. In addition, the associated inner rings have a relatively large radial thickness, which, for a given housing diameter, results in correspondingly short guide vanes and thus a small aerodynamic effective surface. Because the efficiency of the guide vane assembly is limited for these reasons, efforts have been made, in particular for small compressors, to provide other bearing arrangement possibilities for guide vanes. Moreover, a fundamental concern in the design of guide vane assemblies is to minimize leakage flows, which occur in the region of the bearing arrangement and can considerably impair the efficiency of the respective turbomachine. In particular, a resulting renewed inflow can lead to a disruption of the main gas flow and thus lead to flow losses. Such a leakage can be promoted, for example, by gaps that are formed in uptakes and/or in bushings for the bearing pins owing to wear.
Known from EP 2 955 335 A1 is an adjustable guide vane assembly for use in a geometrically small compressor. The guide vanes of the guide vane assembly are hereby mounted directly via their radially inner blade plates in the inner ring.
In EP 2 884 055 A1, for minimization of the installation space, on the one hand, and of leakage flows, on the other hand, an inner ring in which guide vanes are mounted is proposed, for which at least one of the guide vanes has a slip surface radially arranged inside, which is formed essentially perpendicular to the radially directed longitudinal axis of the guide vane. In particular, the radially inner end of the guide vane can have the form of a truncated cone.